How to accurately simulate an anamorphic lens
There is a way to anamorphize the rendered image by controling the aspect ratio values



The values depend on the proportions of the container.

For a 1.33 image the anamorphic pixel ratio should be 2:1 meaning that the image should be squeezed 2 times horizontally (X axis) 

The unsqueezed image would have a format of 2.35:1

For a 16X9 image the anamorphic pixel ratio should be 1.33